The present invention relates to control systems in general, and to voltage regulators in particular.
Voltage regulators, such as DC-to-DC converters, are used to provide stable voltage sources for electronic systems. Efficient DC-to-DC converters are particularly needed for battery management in low power devices, such as laptop computers and mobile phones. Switching voltage regulators (or simply xe2x80x9cswitching regulatorsxe2x80x9d) are known to be an efficient type of DC-to-DC converter. A switching regulator generates an output voltage by converting an input DC voltage into a high frequency voltage, and filtering the high frequency voltage to generate the output DC voltage.
Conventional switching regulators include two switches. One switch is used to alternately couple and decouple an unregulated input DC voltage source, such as a battery, to a load, such as an integrated circuit The other switch is used to alternately couple and decouple the load to ground. An output filter, typically including an inductor and an output capacitor, is coupled between the switches and the load to filter the output of the switches and produce the output DC voltage.
The switches within the switching regulator are opened and closed according to commands from a closed-loop control system. Control systems within DC-to-DC converters, just like control systems generally within any electronic system, need to be stabilized. Care in the design of the control system in a DC-to-DC converter must account for variations of parameters such as the input voltage, filter inductor and capacitor values, switch resistances, printed circuit board parasitics, etc. Sometimes a simple scheme such as voltage feedback alone will stably control a power supply. In other situations, extra margin of stability and higher bandwidth are gained by using current mode control techniques. Still other schemes use hysteresis bands to decide how to control the switches.
In some cases, it is desired to add compensation to improve phase margin of a DC-to-DC regulator. Often phase margin can be improved by using a lag compensator, which lowers the overall bandwidth to boost phase at the crossover frequency. Unfortunately, with lowered bandwidth, DC-to-DC regulators take longer to respond to load current transients, resulting in larger output voltage deviations. As a result, many such systems use extra capacitance in the converter""s output filter to improve transient response. However, using larger capacitors increases the cost of the regulator substantially.
Commercially-available hysteretic controllers trigger certain responses when the output voltage deviates too high, or too low. However, these controllers do not have a beneficial effect on nominal, steady-state performance while the voltage is within the hysteresis bands, and may add design difficulty due to their non-linear behavior.
In one aspect, the invention is directed to a method and computer program product for use in a control system controller having a control loop that includes a storage element, the control loop receiving an output error signal describing an error in the output of the control system. It includes modifying the contents of the storage element according to a predetermined adjustment value when a minimum predetermined excursion occurs in the output error signal; providing a first predetermined gain to the output error signal; providing a second predetermined gain to the output of the control loop; and combining the outputs of the first and second gain elements to produce an output control signal.
Advantages that can be seen in implementations of the invention include one or more of the following. The compensator can add phase margin without requiring extra capacitance, can provide enhance stability during steady-state conditions, and does not degrade transient response.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will become apparent from the description, the drawings, and the claims.